(a) Field of the Invention
The present invention relates to a composition for a positive type photoresist for manufacturing fine circuit patterns such as liquid crystal display circuits or semiconductor integrated circuits and, more particularly, to a composition for a positive type photoresist, including polymer resin, that produces a photoresist layer, photosensitive chemical, and solvents without unpleasant odor.
(b) Description of the Related Art
For producing fine circuit patterns such as those used in liquid crystal display (LCD) circuits or semiconductor integrated circuits, a photoresist composition is uniformly coated or applied on an insulator layer or a conductive metal layer on a substrate. The coated or applied substrate is then exposed through a mask to some form of radiation, such as ultraviolet light, electrons, or X-rays. And the exposed substrate is developed to produce a desired pattern. The patterned photoresist film is used as a mask to remove the insulator layer or the conductive metal layer. The remaining photoresist layer is removed to complete the fine pattern onto the substrate surface. Photoresist compositions are classified into negative and positive types depending on whether the exposed areas of photoresist coating become insoluble or soluble. Recently, positive type photoresist compositions have been preferred because the positive type photoresists can form smaller patterns than the negative type photoresists.
The important properties of photoresist compositions for commercial use are photosensitivities, contrast, resolution, adhesivity to the substrate, remainder ratio and safety.
Photosensitivity refers to the speed how fast the photoresist responds to light. Higher photosensitivity is required, particularly in applications where a number of exposures are performed to form multiple patterns by a repeated process. The other examples are when reduced light is used, like the projection exposure techniques that use light passed through a series of lenses and mono-chromatic filters.
Contrast refers to a ratio between the percentage of film loss in the exposed development area and the percentage of film loss on the unexposed area. Ordinarily, development of an exposed resist coated substrate is continued until the coating on the exposed area is completely dissolved away. Thus, development contrast can be determined simply by measuring the percentage of the film coating loss in the unexposed areas when the exposed coating areas are removed entirely.
Resolution refers to the capability of a photoresist composition how finely to reproduce the mask image utilized during exposure on the developed exposed spaces. In many industrial applications, particularly in the manufacture of LCDs or semiconductor integrated circuits, a photoresist is required to provide a high degree of resolution for very fine line and space widths of 1 xcexc or less.
Generally, photoresist composition includes a polymer resin for producing a photoresist layer, photosensitive chemicals, and a solvent. Various attempts have been made previously to improve the photosensitivity, contrast, resolution, and the safety of positive photoresist compositions. For example, U.S. Pat. No. 3,666,473 discloses the compound of a mixture of two phenol formaldehyde novolak resins together with a typical photosensitive chemical. U.S. Pat. No. 4,115,128 discloses that an organic acid cyclic anhydride was added to the phenolic resin and naphthoquinone diazide photosensitive chemical to increase photosensitivity. U.S. Pat. No. 4,555,069 discloses that novolak resin and o-quninone diazide photosensitivity chemical and propylene glycol alkyl ether acetate solvent are used for higher photosensitivity and for increased safety.
Various solvents have been developed to improve physical properties of the photoresist composition and work safety. For example, ethylene glycol mono ethyl ether acetate or ethyl lactate, propylene glycol mono ethyl ether acetate may be used as solvent. However, the photoresist composition including ethyl lactate exhibits poor adhesivity to the substrate and it is difficult to be uniformly coated on a substrate. Ethylene glycol mono ethyl ether acetate or propylene glycol mono ethyl ether acetate is toxic and generates an unpleasant odor. Accordingly, there is still a need for photoresist compositions that are suitable for various industrial applications, without sacrificing any one of the properties of photosensitivity, contrast, resolution, or solubility of polymer resin.
It is an object of the present invention to provide a composition for a positive type photoresist that exhibits high photosensitivity, remainder ratio, contrast, resolution, and substrate adhesivity for varieties of industrial applications.
It is another object to provide a composition for a positive type photoresist that is safe, without unpleasant odor, and environmentally friendly.
These and other objects may be achieved by a composition for positive type photoresist of the present invention. This composition includes a polymer resin for forming a photoresist layer, a photosensitive chemical that changes solubility of the photoresist layer when exposed to some form of radiation, and a solvent of 3-methoxybutyl acetate and 4-butyrolactone. The polymer resin is preferably a novolak resin and the photosensitive chemical is preferably a diazide-type compound. The ratio of 3-methoxybutylacetate:4-butyrolactone is 60 to 80 parts by weight 3-methoxybutylacetate to 2 to 10 parts by weight 4-butyrolactone.